|
It should be noted that age at blood sampling may affect the accuracy of results. It seems that in blood, sometimes the abnormal cells are eliminated over time. Thus, in an individual cytogenetic analysis in infancy may reveal a higher level of mosaicism than sampling in adolescence.
Blood sampling may give a idea as to the level of mosaicism in the child. This can further complicate genetic counselling since the clinical significance of low levels of chromosomal mosaicism found in blood is unknown. In one case of trisomy 21 mosaicism found on blood, 5% were trisomy 21 cells and the child is reported to be developing normally at 5 years old. In addition, the significance of mosaicism confined to a single organ is unknown (Hahnemann & Vejerslev, 1997) Caution should be used when trying to predict outcome on the basis of percentage of trisomy cells in an infant with mosaicism.
In skin cells (fibroblasts)
As explained above, some individuals have normal chromosomes in peripheral blood sample but are clinically affected. Asymmetric body shape or appearance may be a sign of chromosomal mosaicism. The distribution of the trisomic cell line, which involves generally smaller and less developed cells, can result in an assymetric appearance (Gardner & Sutherland, 1998). An individual with mosaicism in skin cells may show variable patches of skin, such as those that are hypopigmented or hyperpigmented. It should be noted that in skin there could be a variable distribution of the abnormal cells, thus the biopsy of one region may give only normal cells and the biopsy of another region may give abnormal cells.
The finding of chromosomal mosaicism in blood or skin may also arise on a work-up of a child who has been referred to genetics for unexplained congenital anomalies.
As mentioned previously, perhaps many of us carry a tiny and completely unimportant abnormal cell line somewhere in our body. However, even a very minor degree of mosaicism could be important if a crucial tissue carries the abnormal cells.
|